This invention relates to an improved support column for a height-adjustable seat, in particular for office use, and to the seat comprising such a column. Support columns for height-adjustable seats currently comprise a support element constituted by a machined metal tube provided at its lower end with a Morse taper and a closing washer welded to said tube, and a plastics guide bush for the seat raising element, which is controlled by a spring or gas mechanism similar to a shock absorber, which is housed inside the metal tube. This type of column has the drawback of high production cost if considerable accuracy is required in the vertical movement of the raising element. In this respect, numerous mechanical machining operations have to be carried out on the metal tube (turning, inner reaming, tapering of one end, welding) which slow down and considerably complicate the production process. Moreover, the guide bush has to be fixed into the tube by retaining screws, because otherwise it would tend when in use to escape from its seat.